Bug#980921: Pages in HTML5

Hi all
I have added a basic5.wml and template5.wml templates in
/english/templates/debian to start using them in the files that already have
HTML5 tags.

https://salsa.debian.org/webmaster-team/webwml/-/commit/8dc031327d5b4147c02030aac97866283094286d

I have changed mainpage.wml to use the new templates (mainpage.wml is only used
in the homepage).

https://salsa.debian.org/webmaster-team/webwml/-/commit/a10f9519aee4f29278a7c597da8071cd42f9df97


I have updated the recent_list.wml template so the datetime values are produced
in correct format.

https://salsa.debian.org/webmaster-team/webwml/-/commit/2597b5a9d1a8517d803da5ed03b87ac8cf24a11e

I have checked my tests with the homepage with https://validator.w3.org/ and
looks fine.

I'll try to have a look at the validation script and move other pages to use
these html5 templates, and fix the issues that arise.

Kind regards,